[Psychophysics of sweet taste. II. Statistical theory of the stimulus-response behavior of sweet taste receptors]

Considering various conditions of adaptation, the authors determined the Weber discrimination thresholds for the sweet taste of saccharose. When the adaptation to the basic stimulus is maintained and use is made of the differential coefficient behaviour, the discrimination threshold is an exponential function of the concentration. The discrimination threshold is by definition that amount of stimulant per unit of volume which will produce an effect of the magnitude of 1. Consequently, the numbers of moles being substituted, its reciprocal, the probability of obtaining a stimulus response, is greater than 1. A differential equation, namely (formula: see text), can be formulated as the basis of the stimulus-response behaviour of saccharose, the integration of which yields a discrimination characteristic expressed as (formula: see text). S = concentration of the solution as the stimulus intensity; R = stimulus response expressed in steps. The parameter b is the maximum probability of the stimulus response and can be termed substance-specific concentration coefficient. Rm is the maximum step number when the stimulus intensity tends to infinity; it is also substance-specific. As this characteristic involves both the proportional factors and the differential coefficients, it is called P-D characteristic. From this invariant relationship, the static P characteristic for a very slow increase in stimulus intensity can be derived. When the adaptation to the basic stimulus is abolished by mouth rinsing between tests in paired comparisons, the dependence of the discrimination threshold on the concentration is more than exponential. The stimulus-response characteristics obtained with different time-courses of stimulation are approximated by both the Weber-Fechner and the Stevens law.

[Psychophysics of sweet taste. I. Goals and methods of investigation]

With a view to the solution of problems concerned with the consumer's acceptance of foods in which saccharose had been substituted, a discussion is opened on psychologic and physiologic aspects of the measurability of sensory stimulus-sensation relations. The classic method for measuring taste is the determination of the taste discrimination threshold which is also termed least discernible difference. In the lat years, the discrimination threshold has been determined and calculated mainly as the mean concentration (stimulus) difference resulting from the distribution of the tasters according to their efficiency (probit analysis). In contrast, the new method, which is described in detail, is based on the dependence of the probability of a perception of difference upon the intensity which is linear and represents the initial course of a stimulus-response curve. Differences in efficiency in the group of tasters, which is assumed to be homogeneous, are included in the variance of difference frequencies found. The control of the course of the test by sequential analysis and the binomial weighting of the probabilities obtained allow to perform calculations of the discrimination threshold which are largely free from systematic errors; this discrimination threshold is defined as the concentration difference that engenders the arbitrarily defined alternative probability of Pa = 0.75. To minimize the risk of overrating the measurement result, it is suggested to calculate in addition, on the basis of the binomial distribution, the confidence limits of the discrimination threshold. Furthermore, the constant stimulus method for determining the perception of two stimulus intensities of different sweetening agents is adapted, as to performance and calculation, to the new aspects in discrimination threshold determination.

[Sweetness potency of saccharin and cyclamate in hot drinks]

The sweetness potency of sweeteners depends on temperature. At 50 degrees C the 2.4-fold concentration of saccharin and the 1.3-fold of cyclamate respectively is needed to produce the same sweetness (as related to sucrose) as in solutions at 20 degrees C. As well as in water the sweetening power decreases in chinese tea with increasing temperature. Only in case of cyclamate solutions of high sweetness this effect is diminished. In the mathematical description of the relation between stimulus and perception the decrease of the relative sweetness observed can be expressed by a comformable decrease of the concentration coefficient. The effect of temperature on the perception of sweetness can be explained by the Arrhenius' conception. The critical increments are 23 kJ/mol for saccharin and 8 kJ/mol for both cyclamate and fructose.